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From: Sebastian Huber <sh@sourceware.org> To: newlib-cvs@sourceware.org Subject: [newlib-cygwin] Correctly measure system load averages > 1024 Date: Mon, 11 Jul 2022 11:55:35 +0000 (GMT) [thread overview] Message-ID: <20220711115535.869CA385415F@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=27dfb5f33fa4954f6278ae8b82584c269fb6e6ef commit 27dfb5f33fa4954f6278ae8b82584c269fb6e6ef Author: Alan Somers <asomers@FreeBSD.org> Date: Thu May 5 15:35:23 2022 -0600 Correctly measure system load averages > 1024 The old fixed-point arithmetic used for calculating load averages had an overflow at 1024. So on systems with extremely high load, the observed load average would actually fall back to 0 and shoot up again, creating a kind of sawtooth graph. Fix this by using 64-bit math internally, while still reporting the load average to userspace as a 32-bit number. Sponsored by: Axcient Reviewed by: imp Differential Revision: https://reviews.freebsd.org/D35134 Diff: --- newlib/libc/sys/rtems/include/sys/param.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/newlib/libc/sys/rtems/include/sys/param.h b/newlib/libc/sys/rtems/include/sys/param.h index c346453bf..9596ecf52 100644 --- a/newlib/libc/sys/rtems/include/sys/param.h +++ b/newlib/libc/sys/rtems/include/sys/param.h @@ -248,12 +248,12 @@ * Scale factor for scaled integers used to count %cpu time and load avgs. * * The number of CPU `tick's that map to a unique `%age' can be expressed - * by the formula (1 / (2 ^ (FSHIFT - 11))). The maximum load average that - * can be calculated (assuming 32 bits) can be closely approximated using - * the formula (2 ^ (2 * (16 - FSHIFT))) for (FSHIFT < 15). + * by the formula (1 / (2 ^ (FSHIFT - 11))). Since the intermediate + * calculation is done with 64-bit precision, the maximum load average that can + * be calculated is approximately 2^32 / FSCALE. * * For the scheduler to maintain a 1:1 mapping of CPU `tick' to `%age', - * FSHIFT must be at least 11; this gives us a maximum load avg of ~1024. + * FSHIFT must be at least 11. This gives a maximum load avg of 2 million. */ #define FSHIFT 11 /* bits to right of fixed binary point */ #define FSCALE (1<<FSHIFT)
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